Raso lark description

With a tiny population confined to a single, small island off the west coast of Africa, the diminutive Raso lark is perilously close to extinction. The plumage of this species is a mixture of creamy white, black and brown streaks on the upperparts and breast, becoming uniform creamy white on the underparts (2). The head is crowned with a short, erectile crest, while the bill is thick and robust, and slightly longer in the male (2)(3). Juveniles can be readily distinguished from adults by the reddish-brown plumage tones, especially around the ear-coverts and tail, and by the scaled patterning found on the crown and upper back (3).

Related species

Raso lark biology

With its life cycle wholly dependent on infrequent showers of rain, the Raso lark has a particularly precarious existence (2). During periods of drought, one of the few sources of food and water for this species is provided by the small subterranean bulbs of the nutsedges, Cyperus bulbosus or Cyperus cadamosti. In order to reach the bulbs, the Raso lark excavates shallow burrows in the sandy soil using its strong bill (2)(4). Males appear to consume more bulbs than the females, and the largest dominant males usually form territories containing several productive burrows, which they aggressively defend (4)(6). In contrast, females are more reliant on surface food sources such as grass seeds and insects (4). While the difference in bill size between the sexes has previously been thought to account for the differences in feeding behaviour (2)(3)(4), more recent research has shown that this may not be the case (6). Despite its smaller bill size, the female appears to be equally efficient in digging for bulbs, and, as such, its lower bulb intake appears to be due to competitive exclusion from burrowing sites by males. This added obstacle to finding food in Raso Island’s harsh conditions may explain why the Raso lark’s adult population is mostly comprised of males. Not only are the females more likely to starve during droughts, but the increased time spent foraging relative means that less time is spent keeping a look out for potential threats, making losses due to predation more common (6).

Raso lark breeding coincides with the onset of rain showers, with the males courting the females by quietly singing, raising the crest and hopping up and down on the spot with the wings held open. After mating, both sexes collect nesting material such as dried grass, which the female then uses to line a small, three-centimetre deep scrape in the soil, while the male defends the nesting site from intruders. A clutch of up to three eggs may be produced over a period of several days, with individual eggs sometimes laid over a day apart. These are incubated by the female for short, ten-minute periods, interspersed by preening and feeding breaks (4). Few chicks appear to survive to fledging, as newly-hatched chicks and eggs appear to be heavily predated by the Cape Verde giant gecko (Tarentola gigas) (2)(3).

Species with a similar range

Raso lark habitat

Raso Island is a relatively flat, arid island, covered with loose volcanic soil, scattered rocks and no permanent sources of water (4)(5). In order to survive in these inhospitable conditions, the Raso lark is usually found foraging and breeding amongst small patches of vegetation that grow along dry stream beds (2)

Species found in a similar habitat

Raso lark status

Raso lark threats

As a result of the Raso lark’s restricted range and the frequent long periods of drought on Raso Island, its population never numbers more than around 250 individuals (2), and following particularly adverse years may decline to as low as ten breeding pairs (3). Although droughts and population fluctuations have been a natural occurrence throughout Raso Island’s recorded history, there is concern that the effects of climate change may lead to more extreme periods of drought, leading to this species’ extinction (2)(3).

In addition to climate change, human disturbance is a significant threat, as the Raso lark’s burrows are easily trampled upon, and if an alien predator such as the domestic cat were introduced the small population would most likely be rapidly exterminated (2)(3).

Raso lark conservation

Not only is the Raso lark a protected species under Cape Verde law, but Raso Island is classified as a National Park and requires official authorisation to visit (2)(3). Unfortunately, despite these regulations, poor enforcement means that unofficial visits to the island by fishermen and tourists are common (3). A priority for the conservation of this species is, therefore, to raise awareness within the burgeoning tourist industry, and amongst local fishermen, of the need to preserve the island’s fragile ecosystem, avoiding disturbance to the habitat and preventing the introduction of alien species (2).

Such measures can do little to protect the Raso lark from climate change, hence ongoing research is being directed towards monitoring the population, understanding the conditions that promote successful breeding seasons, as well as the possibility of translocating this species to another, more hospitable island (7).

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